We have cloned the gene for the heat-stable enterotoxin STII from a porcine strain of E. coli and determined its DNA sequence. Preliminary data suggest that human isolates of E. coli, Salmonella, and Shigella also contain this STII gene. The STII gene in E. coli is located between two inverted repeat sequences, suggesting that it is associated with a transposable element. The transposability of the STII gene willl be determined and the nature of the insertion sites will be examined. The size of the STII transposon and the sequences essential for transposition will be ascertained. Since the terminal inverted repeat regions bordering the STII gene are large, the possibility that these regions are, themselves, transposons will be investigated. The transposability of the STII gene in other E. coli isolates will be examined. If transposition occurs, then the structure of the transposable elements will be determined. Finally, we will initiate similar studies to determine the presence and structure of STII gene in other species of enterotoxigenic bacteria. The STII genes present in other bacteria will then be assayed for transposability. In this manner, information concerning the molecular nature, the mechanism of dissemination, and the distribution of the E. coli STII gene among bacterial will be obtained.